(1) Field of the Invention
The present invention relates to a method and an apparatus for rewriting data of a control unit for a vehicle, and in particular relates to technology relating to rewriting learning data stored in a control memory of a control unit for a vehicle.
(2) Description of Related Art
Heretofore in a control unit for controlling an actuator of a vehicle engine an operation is carried out such that an engine can be controlled to desired conditions from the time it starts, by storing learning data in a control memory and then controlling the actuator on the basis of the learning data.
For example, in the idle rotation speed control disclosed in Japanese Unexamined Patent Publication No. Hei 4-311642, an actuator for regulating air quantity so that the engine rotation speed at the time of idling corresponds to a target rotation speed, is feedback controlled and a control signal for the actuator at the time when the target rotation speed is attained is stored in the control memory as learning data.
Also, there is the case where a memory that is electrically erasable and programmable using an external tool (for example an EEPROM) is used as the control memory for storing the learning data, the construction being such that the contents of the memory are rewritten without having to exchange the memory.
For example, with the rewritable device disclosed in Japanese Unexamined Patent Publication No. Hei 10-247103, when the learning data is not the initial value, saving of the learning results is achieved by outputting a signal required for prohibiting rewriting with an external tool.
However, in the case where there is a malfunction of the control unit, resulting in the exchange thereof at a maintenance facility, the malfunctioning control unit is taken out of the vehicle and a new control unit is installed in the vehicle. At this time, if the transfer of learning results from the control unit that has been taken out, to the newly installed control unit is not carried out, the need arises to redo the learning in order to correspond to deterioration over time, and differences of the parts. Hence, in the interval until the learning has progressed, there is the likelihood of a reduction in drivability.
Also, in the case where vehicle parts correlating to the learning data (for example, an actuator for regulating auxiliary air quantity in the idle rotation learning control) are exchanged, the learning data no longer conforms to a new actuator, so that it becomes necessary to reset the learning data to the initial value. Although the saving of the learning data progressed is carried out, the configuration is not one where only the learning data correlating to the exchanged vehicle parts is reset to the initial value. Hence the learning data conforming to the vehicle parts before the exchange continues to be used regardless of the vehicle parts that have been exchanged, and all the learning data is reset to the initial value including learning data that need not be reset to the initial value.
The present invention takes into consideration the aforementioned problems with the object of providing a method and an apparatus to appropriately rewrite learning data stored in the control memory of a control unit when vehicle parts exchange is carried out, and to perform appropriate transfer of learning data accompanying exchange of a control unit.
In order to achieve the above object, the present invention is constructed so that at the time of exchanging a vehicle control unit, of the learning data stored in the control memory of the old vehicle control unit, the learning data correlating to the vehicle parts that are exchanged at the same time as exchanging the control unit are corrected to the initial value, and the learning data after correction processing are transferred to the control memory of the new vehicle control unit.
Moreover, the construction is such that at the time of exchanging a vehicle control unit, in a condition with the new vehicle control unit communicably connected to the vehicle mounted old vehicle control unit, when a trigger signal is applied to the old vehicle control unit, the learning data are transferred to the new vehicle control unit.
Other objects and aspects of the present invention will become apparent from the following description of the embodiments given in conjunction with the appended drawings.